This invention relates to the position control of an actuator by means of an electrically controlled servo-valve.
A particular field of application of the invention is that of position control of actuators used in aeronautical engines, especially for metering fuel or for adjusting variable setting angle guide vanes or nozzle flaps in gas turbine engines.
For these applications, the “freezing” of the position of a controlled element is requested in the event of electrical failure at the servo-valve control, to provide safety operation and so that the position occupied before the failure can be found again when it has been possible to rectify the failure.
Servo-valves with what is termed position memory in the event of a failure (or “fail freeze” servo-valves) are well known. In particular, it will be possible to refer to document FR 2 818 331. In this document, the servo-valve comprises a distributor which, in the event of an electrical control failure, comes into a position in which distributor use holes connected to actuator control chambers are closed. A drift from the actuator's “frozen” position is difficult to avoid, due to leaks of the hydraulic fluid contained in the control chambers.